Alterations in Gut Microbiota and Serum Metabolome Are Associated with Postpartum Depression

Background: Postpartum depression (PPD) is a prevalent and debilitating disorder, with increasing evidence implicating the gut microbiota–brain axis. However, integrated alterations in gut microbiota and circulating metabolites in PPD remain insufficiently characterized. Methods: Fecal and serum samples were collected from patients with PPD and healthy controls (HC). Depressive symptoms were assessed using the 17-item Hamilton Depression Rating Scale (HAMD-17). Gut microbiota was analyzed by 16S rRNA sequencing, and serum metabolites were profiled using untargeted LC–MS-based metabolomics. Spearman correlation and receiver operating characteristic (ROC) analyses were performed. Results: A total of 63 participants (42 PPD, 21 HC) were included. Significant alterations in gut microbial composition were observed in PPD, including decreased Faecalibacterium and Akkermansia and increased Ralstonia and Fusobacterium. Candidate differential serum metabolic features, including LPE-related and energy-metabolism-related features, were identified. Exploratory correlation analyses suggested distinct microbiota–metabolite association patterns, and several microbial taxa and serum metabolic features were associated with HAMD-17 scores. ROC analysis showed that several taxa and metabolic features exhibited preliminary discriminative performance with this cohort, although further validation is required. Conclusions: PPD was associated with alterations in gut microbiota composition and exploratory circulating metabolite profiles, potentially involving lipid dysregulation, neuroinflammation, steroid-related metabolism, and neurotoxicity-related pathways. The identified taxa and putatively annotated metabolites should be regarded as exploratory PPD-associated candidates rather than validated biomarkers or mechanistic mediators. Further validation in larger, independent cohorts is warranted. These findings may also inform future microbiota- and nutrition-oriented strategies for postpartum mental health management.